There are various types of flat-panel displays such as liquid crystal displays (LCDs) and electro-chemical displays (ECDs), any of which consumes a small electric power and the scope for applying the flat-panel display becomes wider. Liquid crystal displays, for example, are operable at a very low voltage with a very low electric power consumed. This is incomparable to other display devices. Therefore, liquid crystal displays are applied to a broad range of devices such as audiovisual apparatus, personal computers, television sets, games, and measuring instruments for cars. Now, they are strongly desired to realize a more colorful display.
As conventional liquid crystal color displays there have been a color filter type display, twisted nematic-type display, pleochroic type display or the like. The basic structure of the color filter type display, which is in practical use, is shown in FIG. 6.
Referring to FIG. 6, on both sides of a liquid crystal layer 11, glass substrates 19, 22 are disposed, and or one glass substrate 19, alignment coating 12 for forming an alignment of liquid crystal molecules so as to orient in the predetermined direction, a transparent electrode 14 forming an electrode for each segment, on which RGB ( red, green and blue) color filters 15, 16 and 17 are microscopically arranged in a matrix pattern so as to be coincident with display pixels. Representative ways of arranging the color filters include mosaic like arrangement, stripe arrangement, and triangular like arrangement. Usually, a black matrix is formed intermediate among the RGB color filters 15, 16 and 17 so as to provide the same color tone with the liquid crystal display surface when viewed from the front side. This contributes to improvements in contrast and color purity. On the other glass substrate 22, the alignment coating 13 and a transparent electrode 21 are disposed, and in the outer side of both glass substrates the polarizers 20, 23 are each arranged, further on the lower side of the polarizer a backlight 24 is disposed.
In this arrangement, liquid crystal molecules in the liquid crystal layer 11 are made to orient in a specific direction in response to the voltage applied to the transparent electrodes 14 and 21 provided respectively on opposite sides of the liquid crystal layer 11, whereby the liquid crystal layer 11 transmits light emitted from the backlight. The light passing through the liquid crystal layer 11 further passes through any one of the RGB (red, green and blue) color filters 15 to 17 depending on the subject pixel, then advances a red, green or blue ray. Depending on which pixel light passes through, a desired color is viewed because of a mixture of the color of the subject ray with the color of an adjacent ray, thereby achieving a color display.
The color filter described above comprises a light-shielding layer, colored layer of R, G or B, protective film, and common electrode. The colored layer is formed by dyeing, pigment dispersion, printing, electrodeposition, vapor deposition, or a like technique. Most of color filters in practical use employ dyeing or pigment dispersion. However, these techniques need photolithography and thereby make a large-size color filter expensive. For this reason, the prevalence of conventional flat-panel displays such as liquid crystal color displays is delayed. Therefore, an inexpensive flat-panel color display is being strongly desired. SUMMARY OF THE INVENTION
It is, in view of such circumstances, an object of the present invention to provide a light source for flat-panel color display which does not need a color filter and is, hence, inexpensive.